Unity Decal Shader

Shader "Example/Decal" {
  Properties {
    _MainTex ("Base (RGB)", 2D) = "white" {}
  }
  SubShader {
    Tags { "RenderType"="Opaque" "Queue"="Geometry+1" "ForceNoShadowCasting"="True" }
    LOD 200
    Offset -1, -1
    
    CGPROGRAM
    #pragma surface surf Lambert decal:blend
    
    sampler2D _MainTex;
    
    struct Input {
      float2 uv_MainTex;
    };
    
    void surf (Input IN, inout SurfaceOutput o) {
      half4 c = tex2D (_MainTex, IN.uv_MainTex);
      o.Albedo = c.rgb;
      o.Alpha = c.a;
    }
    ENDCG
  } 

Decal

Decal are commonly used to add details to materials at runtime (bullets impacts are for example). They are a great tool especially in deferred rendering as they alter the GBuffer before it is lit, thus saving on performance.

In a typical scenario Decal should probably be rendered after the opaque objects and should not be a shadow caster as seen in the shaderlab “Tags” in the example below.